Field of the Disclosure
The present disclosure relates to a display device, in which touch sensors are embedded in a pixel array, and a method for driving the same.
Discussion of the Related Art
A user interface (UI) is configured so that users are able to communicate with various electronic devices, and thus, can easily and comfortably control the electronic devices as they desire. Examples of a user interface include a keypad, a keyboard, a mouse, an on-screen display (OSD), and a remote controller having an infrared communication function or a radio frequency (RF) communication function. User interface technology has continuously expanded to increase user's sensibility and handling convenience. The user interface has been recently developed to include touch UI, voice recognition UI, 3D UI, etc.
The touch UI has been essentially adopted in portable information devices, such as smart phones, and expanded to notebook computers, computer monitors, and home appliances. A technology (hereinafter referred to as “in-cell touch sensor technology”) has been recently proposed to embed touch sensors in a pixel array of a display panel. In the in-cell touch sensor technology, the touch sensors may be installed in the display panel without an increase in a thickness of the display panel. The touch sensors are connected to pixels through parasitic capacitances. In order to reduce a mutual influence and crosstalk attributable to coupling between the pixels and the touch sensors, one frame period may be time-divided into a period (hereinafter referred to as “display driving period”), in which the pixels are driven, and a period (hereinafter referred to as a “touch sensor driving period”), in which the touch sensors are driven.
In the in-cell touch sensor technology, electrodes connected to the pixels of the display panel are used as electrodes of the touch sensors. For example, in the in-cell touch sensor technology, a common electrode supplying a common voltage to pixels of a liquid crystal display is segmented, and segmented common electrode patterns are used as the electrodes of the touch sensors.
A parasitic capacitance connected to the in-cell touch sensors increases due to coupling between the in-cell touch sensors and the pixels. When the parasitic capacitance increases, the possibility of crosstalk increases and touch sensitivity and accuracy of touch recognition are deteriorated. A load free driving method has been proposed to reduce an influence of the parasitic capacitance on the touch sensing by the present applicant. The load free driving method is described below with reference to FIG. 1.
Referring to FIG. 1, the load free driving method supplies AC (alternating current) signals LFD1 and LFD2 having the same phase and the same amplitude Vx as a touch driving signal Vdrv to data lines and gate lines of a display panel during a touch sensor driving period, thereby reducing an influence of a parasitic capacitance of a touch sensor on the touch sensing. More specifically, the load free driving method supplies a data voltage Vdata of an input image to the data lines and also supplies a gate pulse (including voltages VGH and VGL) synchronized with the data voltage Vdata to the gate lines during a display driving period, and supplies the AC signals LFD1 and LFD2 synchronized with the touch driving signal Vdrv to the data lines and the gate lines during the touch sensor driving period.
In the load free driving method, because the touch driving signal Vdrv and the AC signals LFD1 and LFD2 having the same phase and the same amplitude are applied to both ends of the parasitic capacitance, the influence of the parasitic capacitance may be excluded. This is because voltages at both ends of the parasitic capacitance simultaneously change, and an amount of charges charged to the parasitic capacitance decreases as a voltage difference between both ends of the parasitic capacitance decreases. According to the load free driving method, an amount of charges charged to the parasitic capacitance is theoretically zero. Therefore, a load free effect recognized as if there is no parasitic capacitance may be obtained.
The load free effect may be obtained when the touch driving signal Vdrv and the AC signals LFD1 and LFD2 have completely the same phase and the same amplitude. However, if the size of the display device increases, sizes of a connector, a cable, a printed circuit board (PCB) line, etc. may increase. Therefore, the phases and the amplitudes of the AC signals LFD1 and LFD2 may be distorted from an initial setting value. The touch driving signal Vdrv and the AC signals LFD1 and LFD2 may be distorted by several variables including a connector contact resistance, a distance difference between the cable and a metal case, etc.
Referring to FIG. 2, the phases of the AC signals LFD1 and LFD2 respectively deviate from the touch driving signal Vdrv by ϕ1 and ϕ2, and the amplitudes of the AC signals LFD1 and LFD2 deviate from the touch driving signal Vdrv by Va. As described above, when there are a phase difference and an amplitude difference between the touch driving signal Vdrv and the AC signals LFD1 and LFD2, the load free effect is reduced and variations of parasitic capacitance may cause touch detection to deteriorate.